fix: Add /chat command handler to trinity_cli

- Added missing /chat command that was shown in help but not implemented
- /chat → Mode: Conversational Chat
- привет → "Привет! Я Trinity — локальный AI-ассистент..."
- hello → "Hello! I'm Trinity — a 100% local AI assistant..."
- 你好 → "你好！我是Trinity — 本地AI助手..."

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: gHashTag

src/vibeec/trinity_cli.zig

@@ -90,7 +90,10 @@ fn printPrompt(state: *CLIState) void {
 }
 
 fn processCommand(state: *CLIState, cmd: []const u8) void {
-    if (std.mem.eql(u8, cmd, "/code")) {
+    if (std.mem.eql(u8, cmd, "/chat")) {
+        state.mode = .Chat;
+        std.debug.print("{s}Mode: Conversational Chat{s}\n", .{ GREEN, RESET });
+    } else if (std.mem.eql(u8, cmd, "/code")) {
         state.mode = .CodeGen;
         std.debug.print("{s}Mode: Code Generation{s}\n", .{ GREEN, RESET });
     } else if (std.mem.eql(u8, cmd, "/reason")) {